In the bonding field, particularly ultrasonic bonding, a figure of merit used to measure the efficiency of the bonding operation is sometimes characterized by power-time-weight. For smaller dimensioned wires adequate scrubbing between the wire and the bonding surface is obtained with a wide latitude in the selectability of the various factors in the figure of merit. However, in attempting to ultrasonically bond larger dimensioned wires it becomes extremely difficult to maintain the power-time-weight factors within the realm of existing equipment while still obtaining reliable ultrasonic bonds.
One solution suggested for obtaining reliable ultrasonic bonds with larger dimensioned wires using state-of-the-art bonding heads is to increase the weight or force factor associated with the bonding tool. In addition to the obvious disadvantage of increasing the weight factor for larger wires, this solution encounters additional problems in that for irregular or nonideal wire dimensions and even great amount of weight or force is required to be exerted by the bonding tool in order to insure scrubbing action.
Prior to describing the objects of the present invention it is to be emphasized that one prior art bonding tool at first glance appears to describe the present invention. That is, the prior art reference calls for a stepped bonding surface. However, upon examination it is to be realized that the stepped bonding surface is merely a compound tool wherein one surface of the step is employed for one bond operation, and then the tool is moved to another bonding site and the other step surface is singularly employed for the bonding operation. This is analogous to a two-headed hammer where one head is employed to drive one nail and the other head is employed for another nailing operation.